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Convert MP4 to WebM

Re-encode MP4 videos as WebM with VP9 or VP8 video and Opus audio for websites and HTML5 players; the conversion happens in your browser.

Drop videos to convertMP4, MOV, MKV, WebM, AVI and more · up to 3 files at once free
Choose videosProcessed on your device — never uploaded
Runs in your browser · no uploadHow it works

How to use MP4 to WebM

  1. 1

    Drop the MP4 videos

    Add up to 3 MP4 (or MOV) files of up to 500 MB and 10 minutes each.

  2. 2

    Keep WebM selected

    Choose High, Balanced or Small quality, and a lower resolution if the clip is meant as a light web background.

  3. 3

    Convert

    The video is re-encoded to VP9 where your browser can encode it, or VP8 otherwise, with Opus sound.

  4. 4

    Download and embed

    Save name.webm and use it in a <video> tag, a Discord or Telegram post, or a WordPress media library.

Limits and Pro

Three MP4 videos at a time, each of up to 500 MB and 10 minutes.

With Pro, batches grow to 500 videos and files to 4 GB and 10 hours. See Pro

About MP4 to WebM

WebM is the royalty-free video format of the web, made by Google for HTML5 video: VP9 or VP8 pictures with Opus or Vorbis sound in a Matroska-based container. Websites use it for autoplaying hero loops, product clips and background videos because VP9 usually gives a smaller file than H.264 at the same quality, every modern browser plays it, and no codec licence is involved. Android, Discord, Telegram and many web apps accept it too.

An MP4 normally contains H.264 video and AAC audio, and WebM can't hold either, so converting means re-encoding both. The picture is encoded as VP9 with your browser's WebCodecs encoder when it offers one, which is the case in current Chrome, Edge and Firefox; if not, the ffmpeg.wasm engine encodes VP8 instead, which is older and a little less efficient but still plays everywhere WebM does. The sound becomes Opus at 160 kbps, which sounds excellent for both music and speech.

For a muted background video, convert, then remove the sound with Mute video to save space and let browsers autoplay it. Every re-encode loses a little detail, so convert from your best original. iPhones, older Safari versions and some TVs still prefer MP4, which is why many sites offer both: keep the MP4 as a fallback source next to the WebM.

Privacy

The MP4 is decoded and re-encoded to WebM in this tab, using WebCodecs through mediabunny or ffmpeg.wasm in a Web Worker. Nothing is uploaded; if the ffmpeg engine is needed, its 31 MB core comes from jsDelivr and carries none of your video.

MP4 to WebM: frequently asked questions

Is WebM smaller than MP4?
With VP9, usually yes: at the same visual quality a VP9 WebM is often around 30% smaller than an H.264 MP4, which helps page speed. VP8, used when your browser can't encode VP9, is closer to H.264 in size. The exact result depends on the video, so compare the sizes shown after conversion and try Balanced if you need it lighter.
Which browsers can encode VP9 here?
Recent Chrome, Edge, Opera and Firefox encode VP9 through WebCodecs, often with hardware help, so conversion is fast. Where VP9 encoding isn't available, such as some Safari versions, the page falls back to ffmpeg.wasm, which encodes VP8 more slowly on the processor. Both kinds of WebM play in current versions of Chrome, Edge, Firefox and Safari.
How do I use the WebM on my website?
Upload the file and add it to a video element, ideally with the original MP4 as a second source for old devices: the browser picks the first format it supports. For a background loop, add the autoplay, muted, loop and playsinline attributes; browsers only autoplay silent videos, so remove the sound first with Mute video to save bandwidth as well.
Does the conversion keep subtitles and chapters?
No. Only the first video and audio track are converted; embedded subtitle tracks, chapters and extra audio languages are left out. For the web, subtitles are best served as a separate WebVTT file through a track element, which you can make or edit with the Subtitle generator, or add to the WebM itself with Add subtitles.
Why does MP4 to WebM take longer than WebM to MKV?
Because MP4 and WebM use different codecs, every frame has to be decoded and compressed again, whereas a WebM going into MKV is only repackaged. Speed depends on your hardware: VP9 through WebCodecs is quick on most computers, while the VP8 fallback in ffmpeg.wasm can take a few times the clip's length. You can keep using the page while it works.

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